Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $213.92   11.569%   $238.6684   $238.67   $238.65   $238.70  
  Purchase #2 $187.57   3.775%   $194.6508   $194.65   $194.65   $194.70  
  Purchase #3 $137.46   5.379%   $144.854   $144.85   $144.85   $144.90  
  Purchase #4 $87.69   11.460%   $97.7393   $97.74   $97.75   $97.70  
  Purchase #5 $79.51   12.560%   $89.4965   $89.50   $89.50   $89.50  
  Purchase #6 $237.41   12.504%   $267.0957   $267.10   $267.10   $267.10  
  Purchase #7 $165.57   10.557%   $183.0492   $183.05   $183.05   $183.00  
  7 purchase totals = $1,109.13       $1,215.5539   $1,215.56   $1,215.55   $1,215.60